A typical heat utilizing apparatus includes a heat pump that includes a compressor, a first heat exchanger, an expansion valve, and a second heat exchanger sequentially connected in a closed circuit by pipes and through which a heat medium flowing through the pipes circulates. For example, a case where the heat utilizing apparatus performs a cooling operation for cooling an indoor space will now be described on the assumption that the heat medium circulates through the heat pump while passing through the compressor, the first heat exchanger, the expansion valve, and the second heat exchanger in that order. In the heat pump, the first heat exchanger allows the heat medium flowing through the pipe to exchange heat with the outside of the heat utilizing apparatus, for example, outdoor air. Then, the expansion valve expands the heat medium flowing through the pipe, so that the heat medium decreases in temperature and thus enters a lower temperature, lower pressure state than before passing through the expansion valve. Then, the second heat exchanger allows the low temperature, low pressure heat medium to exchange heat with the outside of the heat utilizing apparatus. Specifically, the heat exchange in the second heat exchanger causes the low temperature, low pressure heat medium to transfer cooling energy to the indoor space, so that the indoor space is filled with cold air.
In the second heat exchanger, the low temperature, low pressure heat medium increases in temperature by exchanging heat with the outside of the heat utilizing apparatus, so that the heat medium has substantially the same state as that before passing through the expansion valve. Then, the compressor pressurizes the heat medium, so that the heat medium increases in temperature and thus enters a higher temperature, higher pressure state than before passing through the compressor. After that, in the first heat exchanger, the high temperature, high pressure heat medium exchanges heat with the outside of the heat utilizing apparatus. Specifically, in the first heat exchanger, the high temperature, high pressure heat medium releases its heating energy to the outside of the heat utilizing apparatus and receives heat from the outside of the heat utilizing apparatus. In the first heat exchanger, the high temperature, high pressure heat medium decreases in temperature by exchanging heat with the outside of the heat utilizing apparatus, so that the heat medium has substantially the same state as that before passing through the compressor. In other words, the heat medium has substantially the same state as that before passing through the expansion valve. Heat circulates through the heat pump.
With the above-described configuration, the heat pump produces heating energy when the heat pump is intended to produce cooling energy. In other words, the heat pump produces heat intended to be used and heat having a temperature different from the heat intended to be used. In the cooling operation, corresponding to a heat pump normal operation, of the heat utilizing apparatus, as described above, the heating energy produced in addition to the cooling energy used for cooling is rejected as waste heat to the outside of the heat utilizing apparatus through an outdoor unit (refer to, for example, Patent Literature 1). Conversely, when the heat pump is operated to produce heating energy, the heat pump produces cooling energy as well as the heating energy. In a heating operation of the heat utilizing apparatus, the cooling energy produced in addition to the heating energy used for heating is rejected as waste heat to the outside of the heat utilizing apparatus.